Ultrasonic instruments, including both hollow core and solid core elements, are used for the safe and effective treatment of many medical conditions. Ultrasonic instruments, and particularly ultrasonic instruments comprising contact ultrasonic elements, are advantageous because they may be used to cut and/or coagulate tissue using energy in the form of mechanical vibrations transmitted to a surgical end effector at ultrasonic frequencies. Ultrasonic instruments utilizing contact ultrasonic elements are particularly advantageous because of the amount of ultrasonic energy that may be transmitted from an ultrasonic transducer, through a transmission component or waveguide, to the surgical end effector. Such instruments may be used for open or minimally invasive surgical procedures, such as endoscopic or laparoscopic surgical procedures, wherein the end effector is passed through a trocar to reach the surgical site.
Activating or exciting a single or multiple-element end effector of such instruments at ultrasonic frequencies induces longitudinal, transverse or torsional vibratory movement relative to the transmission component that generates localized heat within adjacent tissue, facilitating both cutting and coagulating. Because of the nature of ultrasonic instruments, a particular ultrasonically actuated end effector may be designed to perform numerous functions. Ultrasonic vibrations, when transmitted to organic tissue at suitable energy levels using a suitable end effector, may be used to cut, dissect, separate, lift, transect, elevate, coagulate or cauterize tissue, or to separate or scrape muscle tissue away from bone with or without the assistance of a clamping assembly.
Ultrasonic vibration is induced in the surgical end effector by electrically exciting a transducer, for example. The transducer may be constructed of one or more piezoelectric or magnetostrictive elements located in the instrument hand piece. Vibrations generated by the transducer section are transmitted to the surgical end effector via an ultrasonic transmission component such as a waveguide extending from the transducer section to the surgical end effector. The waveguide and end effector are most preferably designed to resonate at the same frequency as the transducer. Therefore, when an end effector is attached to a transducer the overall system frequency is the same frequency as the transducer itself.
The zero-to-peak amplitude of the longitudinal ultrasonic vibration at the tip, d, of the end effector behaves as a simple sinusoid at the resonant frequency as given by:d=A(x)sin(ωt)  (1)where:
ω=the radian frequency which equals 2π times the cyclic frequency, f; and
A(x)=the zero-to-peak amplitude as a function of position x along the blade.
The longitudinal excursion is defined as the peak-to-peak (p-t-p) amplitude, which is just twice the amplitude of the sine wave or 2A. A(x) varies as a standing wave pattern and is referred to as the displacement curve. At displacement nodes, A(x)=zero and there is no ultrasonic excursion. At antinodes, A(x) is at a local extreme, either a maximum or a minimum (minimum refers to a negative maximum).
Acoustic assemblies may comprise acoustic horns geometrically formed to amplify, attenuate, or transmit the amplitude of the vibrations produced by the piezoelectric or magnetostrictive actuators. Conventional horns generally have two distinct cross-sectional areas, usually with a taper between them, with the larger area, or input area, facing the actuation stack. Conventional horns are configured with a direct transition between the input and output areas. An amplifying acoustic horn (e.g., a fore-bell) is configured as a tapered solid with a larger diameter end (e.g., the input area) adapted to couple directly to the transducer and a smaller diameter end (e.g., the output area) at the tip adapted to couple to the end effector. The tapering cross-sectional area of the horn amplifies the limited displacements generated by the transducer. Vibration actuators operating from acoustic to ultrasonic frequencies generally include three main components. These components include the horn, a stack of piezoelectric or magnetostrictive elements (e.g., a transducer, actuator stack), and a backing material (e.g., an end-bell). The stack of piezoelectric elements is held in compression by a stress bolt that joins the backing material to the horn. The change in area is used to amplify the limited displacement that is induced by the stack.
Solid core ultrasonic instruments may be divided into single-element end effector devices and multiple-element end effector devices. Single-element end effector devices include instruments such as blades, scalpels, hooks, or ball coagulators. Multiple-element end effectors include the single-element end effector in conjunction with a mechanism to press or clamp tissue against the single-element end effector. Multiple-element end effectors comprise clamping scalpels, clamping coagulators or any combination of a clamping assembly with a single-element end effector generally referred to as clamp coagulators. Multiple-element end effectors may be employed when substantial pressure may be necessary to effectively couple ultrasonic energy to the tissue. Such end effectors apply a compressive or biasing force to the tissue to promote faster cutting and coagulation of the tissue, particularly loose and unsupported tissue.
Various design examples of vibration amplifiers, e.g., acoustic horns, are discussed in “Novel Horn Designs for Ultrasonic/Sonic Cleaning Welding, Soldering, Cutting and Drilling”, Proc. SPIE Smart Structures Conference, Vol. 4701, Paper No. 34, San Diego, Calif., March 2002. Additional examples of horn designs are discussed in United States Patent Application Publication US20040047485A1, titled “Folded Horns for Vibration Actuator”. The first reference discusses a folded horn connected to an ultrasonic transducer or actuator and the other end is in contact with the work piece (e.g., an ultrasonic blade or an ultrasonic transmission component or waveguide coupled to the blade). The “distal end” of the folded horn described in the reference, however, is not in contact with the work piece.
There is a need, however, for an end effector comprising one or more folded elements to reduce the overall length of an end effector while remaining in contact with the target tissue. There is also a need for an end effector comprising moveable folded elements. There is also a need for an end effector comprising a folded element located at the distal end that is located neither at a node nor an antinode and operates at an intermediate displacement amplitude.